The Final Fantasy Showdown
The protagonists of each Final Fantasy game with all their ultimate equipment, magic and with a single companion; a party member from their respective game... your choice, preferably the best suited though, meaning that you should pick the best for all, not just the one you'd prefer to see win.)
Here are the main participants:
Firion - Final Fantasy II
Luneth - Final Fantasy III (DS)
Cecil - Final Fantasy IV
Bartz - Final Fantasy V
Terra - Final Fantasy VI
Cloud - Final Fantasy VII
Squall - Final Fantasy VIII
Zidane - Final Fantasy IX
Tidus - Final Fantasy X
Vaan - Final Fantasy XII
Lightning - Final Fantasy XIII
Obviously there are a lot of games in this so if you've not played certain titles simply note it... and leave them out of the fight.
Edit: Just noticed that this is technically against the rules... Heaven knows why 1v1v1 etc aren't allowed though.